kivyMD:如何使用工具栏操作项创建下拉菜单？

from kivymd.app import MDApp
from kivymd.uix.menu import MDDropdownMenu
from kivymd.uix.button import MDIconButton

menu_items = [
    {"text": "选项1", "viewclass": "OneLineListItem"},
    {"text": "选项2", "viewclass": "OneLineListItem"},
    {"text": "选项3", "viewclass": "OneLineListItem"}
]
menu = MDDropdownMenu(
    caller=button,  # 指定触发下拉菜单的按钮
    items=menu_items,
    width_mult=4
)

button = MDIconButton(icon="dots-vertical")
button.bind(on_release=menu.open)

def open_menu(self, button):
    menu.open()